Schottky barrier type solid-state element

ABSTRACT

A Schottky barrier type solid-state element and a method of producing the same, the Schottky barrier type solid-state element comprising a Schottky barrier type element portion consisting of a metallic board and a semiconductor film layer provided on the metallic board, the metallic board being formed of such a metal as can form a Schottky barrier between itself and the semiconductor film layer, and a semiconductor-side terminal electrode provided on the external surface of the semiconductor film layer so as to obtain an ohmic contact therewith, wherein at least the semiconductor film layer is formed by what is called the ionized-cluster-beam deposition process.

BACKGROUND OF THE INVENTION

The present invention relates to a Shottky barrier type solid-stateelement for use in a film-shaped solar battery or the like and a methodof producing the same.

In a method heretofore employed for producing a semiconductorsolid-state element for use in a solar battery or the like, asolid-state element is usually formed by polishing a single-crystal bulkof, for instance, silicon (Si). Therefore, in the conventional method,it is very difficult to form a thin film of semiconductor the thicknessof which is on the order of microns; and even if such a thin film isproduced, the amount of material that can be utilized will be as low asseveral percent or less of the total. Moreover, it is very difficult forany conventional technique to provide an excellent Schottky barrierhighly qualified for use in a solar battery. For instance, it isconsidered to be impossible or almost impossible for the conventionalC.V.D. process, vacuum evaporation process or sputtering process toproduce a high-quality crystalline film and, when a Schottky barrier isto be formed, to control and optimize its microstructure and compositionand to make its density sufficiently high and its resistancesufficiently low.

SUMMARY OF THE INVENTION

Therefore, the primary object of the present invention is to eliminatethe above-mentioned disadvantages of the prior art and to provide aSchottky barrier type solid-state element high in quality andproductivity, thin-film-shaped, light in weight, easy to transport, andsuitable for use in a solar battery, and a method of producing the same.

According to the present invention, there are provided a Shottky barriertype solid-state element and a method of producing the same, theSchottky barrier type solid-state element having a Schottky barrier typeelement portion consisting of a metallic board and a semiconductor filmlayer provided on the surface of the metallic board, the metallic boardbeing formed of such a metal as can form a Schottky barrier betweenitself and the semiconductor film layer, the semiconductor film layerbeing provided on the metallic board so as to form a Schottky barriertherebetween, and a semiconductor-side terminal electrode at leastprovided on the external surface of the semiconductor film layer of theSchottky barrier type element portion so as to obtain an ohmic contacttherewith, wherein at least the semiconductor film layer of the Schottkybarrier type element portion is formed by the ionized-cluster-beamdeposition process which vaporizes a material (a semiconductor, in thiscase) to be deposited to form a vapor, injects the vapor into a vacuumregion of about 10⁻² Torr or less to form aggregates of atoms of thevapor called clusters, bombards the clusters with electrons to ionize atleast a part of the clusters thereby producing ionized clusters, andaccelerates the ionized clusters by an electric field to make themimpinge on a substrate thereby forming a film layer thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will become more apparent fromthe following description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematical sectional view of an example of the evaporationapparatus for carrying out the ionized-cluster-beam deposition processfor use in the method of producing a Schottky barrier type solid-stateelement according to the present invention, showing the principlethereof;

FIG. 2 is a schematical sectional view of the Schottky barrier typesolid-state element according to one embodiment of the presentinvention, showing the essential part thereof for the explanatorypurpose; and

FIG. 3 is a schematical sectional view of the Schottky barrier typesolid-state element according to another embodiment of the presentinvention, showing the essential part thereof for the explanatorypurpose.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, description will be hereinafter made on oneembodiment of the present invention to which the ionized-cluster-beamdeposition process is applied.

Reference numeral 1 designates a substrate on the surface 2 of which asingle-crystal semiconductor film layer 3 made of, e.g., p-type orn-type silicon is deposited. Numeral 4 designates a closed-type cruciblehaving at least an injection nozzle 5. A material 6 of the semiconductorfilm layer 3 to be deposited on the substrate 1, that is, a p-type orn-type semiconductor material, for instance, p-type or n-type silicon isplaced in the crucible 4, which is then heated up to a high temperatureby suitable heating methods such as resistance heating and electronbombardment heating (as shown in FIG. 1) to vaporize the material 6therein to form a vapor 7 the pressure of which is about 10⁻⁶ to severalTorrs. The vapor 7 is then injected from the crucible 4, through thenozzle 5, into a vacuum region 8 kept at a pressure 1/100 or less of thevapor pressure in the crucible 4 and also at about 10⁻² Torr or less. Atthis time, the vapor 7 is converted into aggregates of atoms calledclusters 9 due to supercooling phenomenon caused by adiabatic expansion.One cluster usually consists of about 100 to 2,000 atoms. If one of theatoms constituting each cluster 9 is ionized, an ionized cluster can beformed. Therefore, a filament 10 is provided as a therionic emissionsource to emit electrons, which impinge on the clusters 9 to produceionized clusters 12. The ionized clusters 12, while flying together withthe non-ionized neutral clusters 9 towards the substrate 1 provided inthe route of the clusters, are accelerated by an electric field createdby an acceleration power source 13 connected to electrodes positioned atand/or near the substrate 1, and thereby are brought into collision withthe surface 2 of the substrate 1 to form a film layer 8 thereon.

In the above-mentioned ionized-cluster-beam deposition process whichforms ionized clusters of a material-to-be-deposited and acceleratesthem to let them impinge on a substrate thereby depositing a film layerthereon, the surface 2 of the substrate 1 is at all times kept clean dueto continuous sputter-cleaning action produced by bombardment of theionized clusters 12, and therefore a very clean and highly adhesivedeposition can be achieved. In addition, the ionized clusters 12 areaccelerated with a proper high energy given by a high-voltage electricfield applied, and therefore, when they impinge on the surface 2 of thesubstrate 1, their kinetic energy is partly converted into thermalenergy, which causes a local temperature rise and thereby enables thefilm layer 3 of the depositing material to epitaxially grow on thesurface 2 of the substrate 1. As mentioned above, the self-heatingeffect of the surface of the depositing film layer due to the conversionof the kinetic energy of the clusters into thermal energy canindependently achieve an excellent crystal growth without any particularexternal heating of the substrate 1. However, a suitable combination ofan increase in the kinetic energy of clusters and application ofexternal heating to the substrate will further increase thesingle-crystal area and therefore can made to grow a more excellentepitaxial crystal film layer.

Referring now to FIG. 2, description will be hereinafter made on thefirst embodiment of the Schottky barrier type solid-state element usedas a solar battery according to the present invention and a method ofproducing the same.

Reference numeral 14 designates a thin-sheet-shaped metallic board 14made of such a metal as can form a Schottky barrier between itself and asemiconductor to be deposited thereon. Numeral 16 designates a p-type orn-type semiconductor crystalline film layer deposited on the surface 15of the metallic board 14 by the above-mentioned ionized-cluster-beamdeposition process so that a Schottky barrier may be formedtherebetween. Thus an element portion 17 of a Shottky barrier typesolid-state element 20 used as solar battery is formed, which consistsof the metallic board 14 and the crystalline semiconductor film layer16. In this case, the metallic board 14 and the semiconductor film layer16 correspond, respectively, to the substrate 1 and the depositingmaterial film layer 3 described in the case of the ionized-cluster-beamdeposition process with reference to FIG. 1. The reference numeral 18designates a metallic-board-side terminal electrode coated at a suitableportion on the metallic board 14 where the crystalline film layer 16 isnot coated. In addition, a semiconductor-side terminal electrode 19 isprovided at a suitable portion on the semiconductor film layer 16 coatedon the metallic board 14 so as to form a Schottky barrier therebetween,by depositing thereon a metallic film layer made of such a metal as canestablish an ohmic contact with the material of the semiconductor filmlayer 16 using the above-mentioned ionized-cluster-beam depositionprocess. The stage for forming the metallic-board-side terminalelectrode 18 on the metallic board 14 may be carried out either beforeor after the stage for forming the semiconductor film layer 16 on themetallic board 14, as a matter of course. Moreover, the metallic board14 may be formed so that a part thereof can be used as themetallic-board-side terminal electrode 18, depending upon the size andshape thereof.

The metallic board 14, at least the upper layer thereof, may bepreferably made of gold, chromium, etc. The semiconductor film layer 16provided on the metallic board 14 so as to form a Schottky barriertherebetween may be formed of a p-type or n-type semiconductor and maypreferably have a thickness of several microns to several hundredmicrons. The metallic film layer of the semiconductor-side terminalelectrode 19 provided on the upper surface of the semiconductor filmlayer 16 so as to establish an ohmic contact therebetween may bepreferably made of a metal containing aluminum, indium and others whenthe semiconductor to be in contact therewith is, for instance, p-typesilicon; and a metal containing antimony, etc. when the semiconductor tobe in contact therewith is, for instance, n-type silicon.

As mentioned above, the Schottky barrier type element portion 17 isprovided at the opposite surfaces thereof with terminal electrodes bythe ionized-cluster-beam deposition process disclosed in the aboveembodiment. Accordingly, when the ionized clusters impinge on thedeposition surface, the kinetic energy of the ionized clusters is partlyconverted into thermal energy, and therefore a very good contact can beestablished and, in addition, a sufficient ohmic contact can be obtainedbetween the metal and the semiconductor of the element portion cominginto contact with each other in a heat processing carried out at atemperature far lower than that applied in the case of the prior artsuch as the conventional vacuum evaporation process. From the standpointof the process procedure, this heat processing has an advantage in thatit can be performed either during or after the deposition stage usingthe ionized-cluster-beam deposition process.

Reference numeral 21 designates a reflection preventive film layerproperly formed on the upper surface of the element portion 17. Thereflection preventive film layer 21 provides a light-receiving layer foreffectively absorbing rays incident thereon from the outside, and may beformed by the ionized-cluster-beam deposition process or other variousconventional methods. The metallic film layer of the semiconductor-sideterminal electrode 19 formed on the upper surface of the element portion17 can be provided with the function of the reflection preventive filmlayer 21 concurrently, if the material, conditions, etc. are properlyselected.

Thus a Schottky barrier type solid-state element 20 used as a solarbattery very high in quality can be produced.

In each stage mentioned above in which the above ionized-cluster-beamdeposition process is carried out, it is just the matter of course thatthe processing condictions such as substrate temperature, intensity ofelectron current for ionization and the acceleration voltage for ionizedclusters should be properly selected so that each deposited film layermay be optimized in adhesion, strength, etc.

As to the stage in the above embodiment where the ionized-cluster-beamdeposition process is applied, description has been made on the casewhere the metallic board 14, on which the semiconductor film layer isdeposited so as to form a Schottky barrier therebetween, is made tocorrespond to the substrate 1 referred to in the ionized-cluster-beamdeposition process described with reference to FIG. 1 and where thesemiconductor film layer 16 is deposited on this metallic board 14 toform a Schottky barrier; however, on the contrary, the semiconductorfilm layer 16 may be made to correspond to the above substrate 1, andthe material of the metallic board 14 may be deposited on thissemiconductor film layer 16.

In the above embodiment, a method of producing a Schottky barrier typesolid state element used as a solar battery having amono-Schottky-barrier type element portion is shown which comprises thesteps of depositing a semiconductor film layer on the surface of ametallic board by the ionized-cluster-beam deposition process to form amono-Schottky barrier type element portion, the metallic board beingmade of metal at least at the surface thereof, and fixing terminalelectrodes on the metallic board and the semiconductor film layer,respectively. However, the present invention is not limited to suchembodiment, as a matter of course. For instance, a plurality oflaminated element portions similar to the above element portion may beprovided between the electrodes in ohmic contact therewith to form whatis called the multi-Schottky-barrier type solid-state element, i.e,solar battery, which can be made very thin and highly effective.

Reference is now made to FIG. 3, which is a sectional side view of theessential part of a Schottky barrier type solid-state element used as asolar battery according to another embodiment of the present invention.Description will be hereinafter made on this solid-state element used asa solar battery and a method of producing the same.

Reference numeral 22 designates a film-speed or thin-sheet-shaped orflexible film-shaped substrate board made of various organic substancessuch as polyimide and Mylar, or inorganic insulating materials such asglass and ceramics, or metals. On the upper surface of this substrateboard 22, such a metallic film layer as can establish an an ohmiccontact with a semiconductor film layer to be subsequently depositedthereon is deposited by the ionized-cluster-beam deposition process asdescribed with reference to FIG. 1 to form a semiconductor-side terminalelectrode 23.

After the semiconductor-side terminal electrode 23 is formed, asemiconductor film layer 24 (the thickness of which is, for instance,about several thousand angstroms to several microns) made of n-type orp-type silicon is deposited on the upper surface of the above-mentionedsemiconductor-side terminal electrode 23 in a laminated manner by theionized-cluster-beam deposition process similar to the above-mentioned.In this deposition stage, the substrate board 22 with thesemiconductor-side terminal electrode 23 thereon is made to correspondto the substrate 1 referred to in the description on theionized-cluster-beam deposition process with reference to FIG. 1, andthe semiconductor film layer 25 corresponding to the film layer 3 ofFIG. 1 is deposited on the semiconductor-side terminal electrodeprovided on the substrate board 22, by the ionized-cluster-beamdeposition process.

After the above deposition stage is completed, a metallic board 25, thethickness of which is about several hundred angstroms to severalmicrons, formed of such a metal film layer as can form a Schottkybarrier between itself and the semiconductor film layer 24 is depositedon the upper surface of the semiconductor film layer 24 by theionized-cluster-beam deposition process similar to the above-mentioned.Thus a Schottky barrier type element portion 29, consisting of themetallic board 25 and the semiconductor film layer 24, is formed.

After the above deposition process is completed, a current-collectingmetallic-board-side terminal electrode 26, comb-shaped, wire-shaped orthe like, is provided on the upper surface of the metallic board 25, anda reflection preventive film layer 27 is provided at a proper portion onthe upper surface of the metallic board 25.

As mentioned above, the silicon film layer is formed by theionized-cluster-beam deposition process, in which, when the ionizedclusters impinge on the deposition surface, its kinetic energy is partlyconverted into thermal energy. Therefore, the silicon film layer thusdeposited shows good crystalline properties, and can provide asufficient ohmic contact with the metallic film layer being in contacttherewith, by a heat processing carried out at a temperature far lowerthan that applied in the conventional method.

In each stage mentioned above in which the ionized-cluster-beamdeposition process is carried out, it is just the matter of course thatthe processing conditions such as substrate temperature, intensity ofelectron current for ionization, and acceleration voltage for ionizedclusters should be properly selected according to the substratematerial, the surface condition and depositing material of each filmlayer, etc. so that each deposited film layer may be optimized inquality, adhesion, strength, etc.

The embodiment shown above is concerned with a Schottky barrier typesolid-state element having a set of laminated film layers. Moreparticularly, as mentioned above, the method of producing such asolid-state element comprises the steps of forming a semiconductor-sideterminal electrode, formed of such a metal film layer as can establishan ohmic contact with a semiconductor to be subsequently depositedthereon, on a substrate board; forming a semiconductor film layer on thesemiconductor-side terminal electrode; and providing a metallic board,formed of such a metallic film layer as can form a Schottky barrierbetween itself and the semiconductor film layer, on the semiconductorfilm layer. However, the present invention is not limited to thisembodiment, and the above sets of steps may be repeated to form aplurality of sets of laminated film layers, as a matter of course. Inthis manner, a solid-state element having a further increasedphoto-electric conversion efficiency, etc. can be produced.

The Schottky barrier type solid-state element thus produced has aconstruction in which a very high-quality and film-shaped Schottkybarrier type semiconductor element is provided on the substrate board22. Therefore, if the substrate board 22 is formed of a flexible film,the solid-state element as a whole can be made sufficiently flexible andtherefore free from fatigue due to folding or rolling-up.

In the above embodiment of the present invention, theionized-cluster-beam deposition process is used for each of thedeposition stages of the semiconductor-side terminal electrode 23, thesemiconductor film layer 24 and the metallic board 25, and thereby theadhesion of each film layer is remarkably increased and the productquality is much improved. In this case, it is necessary that theionized-cluster-beam deposition process should be applied at least tothe deposition stage of the semiconductor film layer 24.

As mentioned above, the substrate board 22 is preferably made ofthin-sheet-shaped or flexible film-shaped organic substance such asMylar or Polyimide, or thin-sheet-shaped inorganic substance such asglass or ceramics, or film-shaped or thin-sheet-shaped metal. Of thesevarious shapes and materials, a proper one may be selected according tothe purpose and use of the Schottky barrier type solid-state element tobe produced.

The metallic film of the semiconductor-side terminal electrode 23 ispreferably made of a metal containing, for instance, aluminum and indiumwhen the semiconductor film layer 24 in contact therewith is of p-typesilicon, and a metal containing, for instance, antimony when thesemiconductor film layer 24 is of n-type silicon.

The metallic board 25 is preferably made of gold, chromium, etc.

The semiconductor-side terminal electrode 23 and the metallic board 25are in ohmic contact with the semiconductor film layer 24 and themetallic-board-side terminal electrode 26, respectively.

The reflection preventive film layer 27 shown in the above embodiment isprovided to form a light-receiving surface for effectively absorbingrays incident thereon from the outside, when the solid-state element isused as a solar battery; and is formed on the upper surface of thesolid-state element by the ionized-cluster-beam deposition process ofthe present invention or other various methods. Instead of providing thereflection preventive film layer 27, the metallic-board-side terminalelectrode 26 may be so formed that it can concurrently perform thereflection preventive function.

It will apparent from the foregoing description that the presentinvention is concerned with the Schottky barrier type solid-stateelement which is produced by depositing at least the semiconductor filmlayer in a laminated manner by the ionized-cluster-beam depositionprocess and is highly suitable for use in a solar battery or others.

Various features and effects of the present invention are enumerated asfollows:

(1) In the ionized-cluster-beam deposition process used in the presentinvention, the substrate surface is at all times kept clean due to thesputter-cleaning action of ionized clusters during deposition, andtherefore a deposited film can be made very high in adhesion andquality.

(2) Since the deposition process of the present invention acceleratesthe ionized clusters with a suitable high energy created by ahigh-voltage electric field applied, it can produce what is called theself-heating effect of the surface of the depositing film layer whichcreates a local temperature rise due to partial conversion of thekinetic energy of the ionized clusters into thermal energy when theionized clusters impinge on the substrate, and also it can produce whatis called the migration effect which breaks up the ionized andnon-ionized clusters into individual atomic particles and spreads themover the surface of the depositing film layer by the energy they have atthe time of impact. Therefore, the deposition process of the presentinvention can achieve an excellent crystal growth of the depositingmaterial.

Furthermore, in the present invention, the crystal growth of thedepositing film layer is carried out while being controlled by thecrystalline properties of the substrate, and therefore a Schottkybarrier type solid-state element excellent in quality and crystallineproperties can be produced.

(3) The deposition process of the present invention can control theacceleration voltage and current during deposition so that themicrostructure and composition of the deposition boundary may beoptimized. Accordingly, it can increase the deposition density anddecrease the resistance at the deposition surface, and therefore canproduce a solid-state element whose construction and composition is mostsuitable for use in a solar battery.

(4) The thickness of the film layer to be deposited on the substrate soas to form a Schottky barrier therebetween can be controlled by properlyadjusting the processing conditions during deposition. Therefore, thethickness of the semiconductor film layer positioned upper than thejunction, i.e., the Schottky barrier portion can be made less than thatformed by the conventional methods. As a result, the wavelengthsensitivity range for incident rays is widened and the photovoltaicconversion efficiency is improved.

(5) The deposition process of the present invention for forming then-type or p-type semiconductor film layer can achieve the concentrationcontrol of the depositing material during deposition, which has beendifficult to achieve by the prior art. As a result, the presentinvention can produce a high-performance solid-state element which caneffectively take out charged particles produced by light irradiation.

(6) If the terminal electrode provided on the element portion is formedalso by the ionized-cluster-beam deposition process as mentioned in theabove embodiment, heat processing for obtaining an ohmic contacttherebetween can be carried out at a temperature far lower than thatapplied in the prior art, and thereby can easily provide a connectiontherebetween with a sufficient ohmic contact, resulting in ahigh-quality product.

(7) As shown in the embodiment of the present invention, a flexibleSchottky barrier type solid-state element, almost impossible to obtainby the prior art, can be produced by forming a film-shaped semiconductorelement on a flexible organic film using the ionized-cluster-beamdeposition process. The solid-state element thus produced can save itsraw materials, and is light in weight, small in size and flexible; andcan be folded or rolled up into a compact size, and therefore is easy tohandle, transport, store, etc.

(8) The present invention can achieve metal-to-metal multi-layer bondingwith strong adhesion, which is considered impossible to achieve by theconventional evaporation processes because of weak adhesion. Especiallywhen the solid-state element is to be used as a solar battery, amulti-layer film suitable for preventing the reflection of incident rayscan be formed.

(9) In the above-mentioned embodiment, description was made on the casewhere silicon was used as semiconductor. However, the semiconductor thatcan be used in this invention is not limited to silicon alone. Besidessilicon, this invention can use other element semiconductors andcompound semiconductors such as Ge, GaAs, InP and CdTe to produce aSchottky barrier type solid-state element. When a compound semiconductoris used, the compound semiconductor itself is not necessarily requiredto be put in the closed type crucible, and a suitable mixture ofcomponent elements of the compound semiconductor may be put therein.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A flexible Schottky barrier type solid-stateelement comprising:a flexible film substrate board; a first metallicfilm layer deposited on said flexible film substrate board by theionized-cluster-beam deposition process wherein a material to bedeposited is vaporized into a vapor, injected into a vacuum region ofabout 10⁻² Torr or less to form aggregates of said vapor calledclusters, said clusters are bombarded with electrons to produce ionizedclusters, and said ionized clusters are accelerated by an electric fieldsuch that they impinge on a surface, thereby forming a film layer ofsaid material on said surface, said first metallic film layer forming anohmic contact semiconductor-side terminal electrode; a semiconductorfilm layer deposited on said first metallic film layer by saidionized-cluster-beam deposition process, a second metallic film layerdeposited on said semiconductor film layer by said ionized-cluster-beamdeposition process, said second metallic film layer and saidsemiconductor film layer forming a Schottky barrier at the boundarytherebetween; a current-collecting metallic-board-side terminalelectrode provided on one portion of said second metallic film; and areflection preventative film layer provided on another portion of saidsecond metallic film; whereby said Schottky solid state element can befolded or rolled into a compact size.